The Colorado State University Plant Diagnostic Clinic blog serves as an information resource on disease and insect problems or questions that we see in the clinic or get asked frequently.

Thursday, November 18, 2010

Updated MPB Information

I thought a recent post by Dave Leatherman, retired CSFS Entomologist, regarding Mountain Pine Beetle would be beneficial as an update on the behavior of the beetle along the Front Range and questions we are receiving regarding when to spray.

"If less than a full compliment of beetles hits an urban tree (i.e. an 'unsuccessful' attack from the viewpoint of the beetle), two patterns have been common the last several years: 1. a band of pitch tubes at mid-trunk, with very few on the basal and upper parts of the trunk, or 2. a gradation of pitch tubes, heaviest at the base, fizzling out about 10 feet above the ground.

The great, great majority of such trees survive, at least the initial attack. These sorts of trees, however, do seem prone to re-attack, sometimes later in the same season, sometimes the following summer. If the trees have high value, rigorous inspection to determine the success of the attack is in order. IF the tree will not die from the attack in question, preventive spraying is warranted. The historical spray timetables have become problematic and spraying anytime during the April to early November period might be warranted, depending on the specific circumstances and wishes of the consumer.

Three things seem clear: 1) the flight season of the beetle is not just late July thru early August anymore (more like April thru early November, with two peaks, one in July-early Aug, and the other mid Oct-early Nov), 2) with the flying beetle population being diluted at any one time over a period of month, successful attacks resulting from a single attack are fairly rare among urban trees, and 3) foliage fading in relation to when observers first see pitch tubes is all out of whack.

For urban areas in CO, NE, and WY and the MPB attacked trees I have seen of late, the following statements apply:

The hosts are overwhelmingly either Scots or Ponderosa pine, the pitch tubes are often large and 'runny' (as would be characteristic of unsuccessful, 'pitch-out' type tubes);

IF the attacked trees die, they didn't die of a single attack; most attacked trees display pitch tubes of varying hardness (indicating initial and later attacks);

IF the attacks are successful and result in a big emergence of beetles, the trees are usually still green-needled (at least not obviously brown) when this occurs;

Emergence is usually in October or November (but sometimes 'on schedule' in July-August);

Relying solely on external evidence is more dangerous than ever because of the above;

A hatchet/under-bark-peek is more needed than ever to make a proper diagnosis (and because of the preponderance of strip attacks, looking under the bark on more than one side of the tree is a wise move).

In urban areas, assuming the trees are of suitable diameter (6 inches or more at breast height), I would put pines into three categores: Likely to be attacked, sometimes attacked, and rarely attacked. The likely to be attacked pines are Scots, Ponderosa and Lodgepole. The sometimes attacked would be Limber and Bristlecone. The rarely attacked pines are Austrian, Mugo, Pinyon, Spruce and other pines."